The overall objective of this research program is better understanding of the human enzyme system involved in alcohol metabolism to find out whether any components of the system are different in the alcoholic. Two isoenzymes of aldehyde dehydrogenase (E1 and E2) have been isolated and shown to be similar in molecular weight, amino acid composition, and number and size of subunits, yet different in catalytic properties and disulfiram inhibition. We have also shown that E1 and E2 differ in structure: E1 and E2 are heterotetramers with no common subunits, showing substantial lack of sequence homology. Differences in interaction with coenzyme between E1 and E2 are observed. Purification of E3 isoenzyme from human liver to apparent homogeneity has been achieved. Work in progress is concerned with identification and characterization of aldehyde dehydrogenase isoenzymes and sequences of their active site peptides. Attempts are being made to develop a two-dimensional system for identification of isoenzyme content and composition of human liver alcohol dehydrogenase, which consists of at least 10 isoenzymes superimposing with each other in one-dimensional systems. Our goals for the coming year include further characterization of human liver aldehyde dehydrogenases E1, E2 and E3 and investigation of aldehyde dehydrogenase content and composition of organs other than liver. When two-dimensional electrophoresis for alcohol dehydrogenase is developed, alcohol dehydrogenase content and composition will be compared with that of aldehyde dehydrogenase in individual human livers. The results will be correlated with the individual's life history related to alcohol consumption.